Modular welding guns

ABSTRACT

An actuator designed for use with a welding gun of the type having a first electrode movable in a straight line toward and away from a second electrode supported by a welding arm. The actuator includes a housing with a first and second end. A bushing with a generally square opening defined therethrough is supported in the first end of the housing. An actuator rod extends through the square opening in the bushing and has a first end inside the housing and a second end disposed external to the housing. The actuator rod has an external surface with a generally square cross section such that the external surface engages the square opening to prevent rotary motion of the rod with respect to the housing. A drive mechanism is disposed in the housing and is operable to move the rod with respect to the housing. The drive mechanism may be a pneumatic actuator or a rotary screw drive.

REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/641,264, filed Aug. 17, 2000, now U.S. Pat. No. 6,596,958,which claims priority from U.S. provisional patent application Ser. No.60/149,337, filed Aug. 17, 1999, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to spot welding guns and, morespecifically, to weld guns that are constructed from modular components.

BACKGROUND OF THE INVENTION

Traditional spot welding guns are usually custom manufactured for theirintended application. These custom weld guns include welding arms thatare moved by some type of actuator, such as a pneumatic or servoactuator. The welding arms, yokes, and pivots are often customconfigured and may be part of a custom casting including the arms,yokes, pivot supports, and actuator arms. Obviously, custom castingportions of the weld gun raises the cost and complexity of the gun andincreases the lead time required for providing the gun for a specificapplication. In light of this, there is a need for a modular approach tothe design and construction of spot welding guns.

SUMMARY OF THE INVENTION

The present invention improves on the prior art by providing a modularwelding gun including a frame and an upper and lower yoke that are bothinterconnected with the frame. At least one of the yokes is movable withrespect to the frame. An upper weld arm has a first end that isremovably interconnected with an upper yoke and a second end which isconfigured to support an electrode. A lower arm has a first endremovably interconnected with the lower yoke, and a second endconfigured to support an electrode. An actuator is operable to move themovably yoke between a welding position and a rest position.

According to the further aspects of the present invention, an actuatoris provided with non-rotate features. The actuator is for use with awelding gun of the type having a first electrode movable in a straightline toward and away from a second electrode supported by a welding arm.The actuator includes a housing with a first and a second end. A bushingwith a generally square opening defined therethrough is supported in thefirst end of the housing. An actuator rod extends through the squareopening in the bushing and has a first end disposed inside the housingand a second end disposed external to the housing. The actuator rod hasan external surface with a generally square cross section such that theexternal surface engages the square opening to prevent rotary motion ofthe rod with respect to the housing. A drive mechanism disposed in thehousing is operable to move the rod with respect to the housing. Thedrive mechanism may be either pneumatic or mechanical.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of a scissors-typemodular weld gun according to the present invention;

FIG. 2 is a perspective view of the weld gun of FIG. 1 showing theopposite side;

FIG. 3 is yet another perspective view of the weld gun of FIGS. 1 and 2;

FIG. 4 is a side elevational view of the weld gun of FIGS. 1-3;

FIG. 5 is a perspective view of a second embodiment of a modularscissors-type servo-actuated welding gun according to the presentinvention;

FIG. 6 is a perspective view of the weld gun of FIG. 5 showing the otherside;

FIG. 7 is yet another perspective of the weld gun of FIGS. 5 and 6;

FIG. 8 is a side elevational view of the welding gun of FIGS. 5-7;

FIG. 9 is a perspective view of the third embodiment of scissors-typewelding gun according to the present invention;

FIG. 10 is a perspective view of the welding gun of FIG. 9 showing theother side;

FIG. 11 is yet another perspective of the welding gun of FIGS. 9 and 10;

FIG. 12 is a side elevations view of the welding gun of FIGS. 9-11;

FIG. 13 is a perspective view of the fourth embodiment of welding gunaccording to the present invention;

FIG. 14 is a perspective view of the welding gun of FIG. 13 showing theother side;

FIG. 15 is a yet another perspective of the welding gun of FIGS. 13 and14;

FIG. 16 is a side elevational view of the welding gun of FIGS. 13-15;

FIG. 17 is a perspective view of the fifth embodiment of welding gunaccording to the present invention;

FIG. 18 is a perspective view of the welding gun of FIG. 17 showing theother side;

FIG. 19 is a yet another perspective of the welding gun of FIGS. 17 and18;

FIG. 20 is a side elevational view of the welding gun of FIGS. 17-19;

FIG. 21 is a perspective view of the sixth embodiment of welding gunaccording to the present invention;

FIG. 22 is a perspective view of the welding gun of FIG. 21 showing theother side;

FIG. 23 is a yet another perspective of the welding gun of FIGS. 21 and22;

FIG. 24 is a side elevational view of the welding gun of FIGS. 21-23;

FIG. 25 is a perspective view of the seventh embodiment of welding gunaccording to the present invention;

FIG. 26 is a cross-sectional view showing the construction of thebearing assembly and the interconnection between the modular weld armsand the upper and lower yokes, taken along lines 26—26 in FIG. 25;

FIG. 27 is a perspective view of the eighth embodiment of welding gunaccording to the present invention;

FIG. 28 is a side elevational view of the welding gun of FIGS. 27;

FIG. 29 is an additional perspective of the welding gun of FIGS. 27 and28;

FIG. 30 is yet another perspective view of the welding gun of FIGS.27-29;

FIG. 31 is a perspective view of the ninth embodiment of welding gunaccording to the present invention;

FIG. 32 is a side elevational view of the welding gun of FIG. 31;

FIG. 33 is another perspective view of the welding gun of FIGS. 31 and32;

FIG. 34 is yet another perspective view of the welding gun of FIGS.31-33;

FIG. 35 is a perspective view of a servo actuator according to a furtheraspect of the present invention;

FIG. 36 is an additional perspective view of the servo actuator of FIG.35 showing the other side;

FIG. 37 is yet another perspective view of the servo actuator of FIGS.35 and 36;

FIG. 38 is a side elevational view of the servo actuator of FIGS. 35-37;

FIG. 39 is a cross-sectional view of a servo actuator of FIGS. 35-38;

FIG. 40 is a detailed view of the actuator end of the servo actuator ofFIG. 39;

FIG. 41 is a cross-sectional view of an alternative embodiment of aservo actuator according to the present invention;

FIG. 42 is an exploded view of the servo actuator of FIG. 41;

FIG. 43 is a perspective view of another embodiment of a servo actuatoraccording to the present invention;

FIG. 44 is a side elevational view of the servo actuator of FIG. 43;

FIG. 45 is another perspective view of the servo actuator of FIGS. 43and 44;

FIG. 46 is yet another perspective view of the servo actuator of FIGS.43-45;

FIG. 47 is a perspective view of yet another alternative embodiment of aservo actuator according to the present invention;

FIG. 48 is another perspective view of the servo actuator of FIG. 47;

FIG. 49 is yet another perspective view of the servo actuator of FIGS.47 and 48;

FIG. 50 is a side elevational view of the servo actuator of FIGS. 47-49;

FIG. 51 is a perspective view of a pneumatic actuator, with non-rotatefeatures, for use with the present invention;

FIG. 52 is a cross-sectional view of a pneumatic actuator, withnon-rotate features, for use with the present invention; and

FIG. 53 is a perspective view of a bushing for use with the actuatorsaccording to the present invention, with a square orifice definedthrough the bushing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1-4, a scissors type modular welding gun according tothe present invention is generally shown at 10. This embodiment has anupper weld arm 12 and a lower weld arm 14 which are pivotallyinterconnected by fulcrum assembly 16. As shown, the fulcrum assemblyincludes an upper yoke 18, a lower yoke 20 and an isolating bearingassembly 22 that pivotally interconnects the yokes 18 and 20. The upperweld arm 12 clamps to the upper yoke 18 for movement therewith. Anactuator arm 24 also clamps to the upper yoke 18 so that the upper weldarm 12, the upper yoke 18, and the actuator arm 24 move as a singleunit. In prior approaches to constructing weld guns, the upper yoke 18,upper weld arm 12, and actuator arm 24 would be cast as a single unitrequiring a custom casting. In the present invention, the upper yoke isformed from a flat piece of metal with standard bolts interconnecting itwith the upper weld arm 12 and the actuator arm 24. The upper weld arm12 is formed from a piece of copper bar stock, and is clamped to theupper yoke 18. Likewise, the actuator arm 24 is cut from a piece ofaluminum stock and bolted to the upper yoke 18.

Likewise, the lower yoke 20 is bolted to the lower weld arm 14, which isformed from a piece of bar stock. Once again, traditional weld gunsinclude a custom cast lower arm and yoke assembly whereas the presentinvention allows the use of standardized parts which may be boltedtogether to form a complete assembly.

Another difference between the present invention and the prior art isthe construction of the bearing assembly 22. In traditional spot weldingscissors type guns, the upper and lower yokes surround the bearing fromboth sides making access to the bearing for servicing difficult. In thepresent invention, the upper yoke 18 and lower yoke 22 lie side by sideand the bearing assembly 22 pivotally interconnects them in a cantileverfashion. As shown, a through bolt 26 passes through the center of thebearing assembly to interconnect the upper yoke 18 and lower yoke 20.This greatly simplifies maintenance since the bearing assembly 20 may bedisassembled using readily available wrenches.

The weld gun of FIGS. 1-4 also includes a main frame 28 which includesan integral robot mount 30 for mounting the weld gun 10 to a robot. Thefulcrum assembly mounts to the main frame 28, allowing the upper weldarm 12 to pivot relative thereto. The lower yoke 20 is also mounted tothe main frame so that the lower arm does not move relative to the mainframe. Alternatively, the lower arm may also pivot relative to theframe. A modular servo actuator 32 also mounts to the main frame 28 andis positioned behind the weld arms 12 and 14. The servo actuator 32 actsto move the actuator arm 24 upwardly and downwardly, thereby pivotingthe upper weld arm 12 as required to open and close the electrodes 13and 15. As shown, the servo actuator 32 has a fulcrum mount 34 allowingit to pivot slightly relative to the main frame 28 as it moves the upperweld arm 12. The main frame 28, including the robot mount 30 and theportion supporting the fulcrum mount 34 of the servo actuator, is allconstructed from standardized components which bolt or weld together toform a complete assembly. Again, this is simpler than the prior artapproach in which the main frame may be cast or fabricated to includethe various mounting surfaces necessary. Also shown in FIGS. 1-4 is atransformer 36 which also mounts to the main frame 28. As will be clearto those of skill in the art, the transformer 36 may also be remotelymounted, depending on the application.

Obviously, in order to weld using the welding gun of FIGS. 1-4,electrical current must be conducted to or from the electrodes 13 and15. As best show in FIG. 2, a flexible shunt 40 interconnects the upperweld arm 12 with the transformer 36. A modular shunt clamp 42 bolts tothe upper weld arm adjacent the upper yoke 18 and interconnects with theflexible shunt 40. As will be clear to those of skill in the art, theshunt clamp 42 may be clamped to the upper weld arm 12 at variouspositions along its length, depending on the application. Because thelower weld arm 14 is stationary in this embodiment, a non-flexible shunt44 extends between the transformer 36 and a second modular shunt clamp46 which bolts to the lower weld arm 14 adjacent the lower yoke 20. Inthis embodiment, the modular weld arms 12 and 14 are shown as bar stockhaving a circular cross-section that has “squared-off” where they boltto the shunt clamps 42 and 46 in the upper and lower yokes 18 and 20.Alternatively, the weld arms 12 and 14 may have a squared-offcross-section throughout their length.

Referring now to FIGS. 5-8, a second embodiment of a modular scissorstype, servo actuated, welding gun is generally shown at 50. Thisembodiment differs from the previous embodiment in that the yokes 52 and54 are taller and the weld arms 56 and 58 are longer. This weld gun 50is adapted for a different application which requires a wider spacing inbetween the upper and lower arms 56 and 58 and a greater reach betweenthe yokes 52 and 54 and the electrodes 60 and 62. By comparing the firstembodiment and the second embodiment, it can be seen that many of thecomponents are the same or similar. That is, each are formed frommodular components which may be interchanged in order to change theconfiguration of the overall assemblies. In the second embodiment,taller yokes 52 and 54 are used and longer pieces of bar stock are usedto form the arms 56 and 58. The bearing assembly 64 is similar and theactuator arm 66 is longer. As will be clear to those of skill in theart, components from the first embodiment and second embodiment may beinterchanged so as to form other configurations of weld guns. Also, avariety of actuators may be bolted in place of the servo actuatorsillustrated so that the weld guns may work with other systems. Anotherdifference between the second weld gun 50 and the first weld gun 10, isthat the second weld gun 50 is designed to use a remote transformer, notshown, instead of one mounted to the gun. The necessary shunts forinterconnecting with the transformer are not illustrated in theseFigures.

Referring now to FIGS. 9-12, a third embodiment of a weld gun accordingto the present invention is generally shown at 70. This embodiment issimilar to the previous embodiments in that it is constructed frommodular components to make a complete working assembly. However, itdiffers in that it includes a pneumatic actuator rather than a servoactuator. Therefore, both an upper actuator arm 72 and a lower actuatorarm 74 extend rearwardly from the fulcrum assembly 76 that pivotallyinterconnects the upper weld arm 78 and the lower weld arm 80. Apneumatic cylinder 82 is disposed between the ends of the upper andlower actuator arms 72 and 74 so that when the cylinder 82 is actuatedand extended, as shown, the actuator arms 72 and 74 are spread apartcausing the welding arms 70 and 80 to be pushed together. Once again, aswill be clear to those of skill in the art, many of the same componentsare used to construct this gun as in the previous embodiments. Becausethis gun 70 includes a pneumatic actuator, it also includes apositioning cylinder 84 which mounts between the frame 86 and anextension to the upper actuator arm 72. The positioning cylinder 84 isused to position the upper weld arm 78 relative to the frame 86 so thata robot, to which the gun 70 is mounted, may position the upper weldingarm in a known position. Otherwise, the robot is unable to determine theexact positions of the upper and lower electrodes relative to the frame.This embodiment also is designed for use with a remote transformer andincludes a robot mount 88 for mounting the gun to a robot.

Referring now to FIGS. 13-16, a fourth embodiment of a weld gunaccording to the present invention is generally shown at 90. Thisembodiment is similar to the third embodiment except that it is adaptedto be a portable weld gun. For this reason, it includes a support member92 so that the weld gun 90 may be hung from a welder support. It alsoincludes handles 94 and 96 with controls 98 so that an operator maymanually control the weld gun. Also, because the gun is designed forportable use, it does not have a positioning cylinder. Once again, thegun 90 is constructed from a variety of modular components to create acomplete operating assembly.

Referring now to FIGS. 17-20, a fifth embodiment of a modular weld gunaccording to the present invention is generally shown at 100. This gun100 is a further example of a weld gun constructed from modularcomponents. In this embodiment, smaller and shorter weld arms are usedand the yokes are more compact. This embodiment includes a pneumaticactuator and a positioning cylinder and an integral transformer.

Referring now to FIGS. 21-24, a sixth embodiment of a modular weld gunaccording to the present invention is generally shown at 102. Like theearlier embodiments, this embodiment is formed from a variety of modularcomponents. Unlike the earlier embodiments, the upper weld arm 104 isbent so as to suit a different application. Also, this gun is configuredsuch that the lower weld arm 106 is the arm which moves rather than theupper arm 104. This embodiment again illustrates the benefits of thepresent invention which are realized by the combination of modularcomponents. To provide the different configuration, similar componentsare assembled in a different manner. Also, the bar stock upper arm 104provides the benefit that the arm may be bent to the configurationnecessary. If later a straight upper arm is desired, the bent upper arm104 may be unbolted and replaced with a different configuration. This isa benefit to all the configurations in that components may be unboltedfor replacement as necessary to maintain or reconfigure the gun.

Referring now to FIGS. 25 and 26, a seventh embodiment of a modularwelding gun according to the present invention is generally shown at110. The welding gun 110 is a scissors-type arrangement having an upperwelding arm 112 and a lower welding arm 114 pivotally interconnected byfulcrum assembly 111. The fulcrum assembly includes an upper yoke 113and a lower yoke 115 and an isolating bearing assembly 116. The entireassembly is supported by a hanger 117 which interconnects with thebearing assembly 116. FIG. 26 is a cross-sectional view showing theconstruction of the bearing assembly 116 and the upper yoke 113 andlower yoke 115, as well as the interconnection between the yokes and theweld arms. In this embodiment, the weld arms 112 and 114 have generallyrectangular cross-sections throughout their length. Alternatively, theymay be circular throughout part or all of their length. As shown, theupper yoke 113 includes a front plate 107 and a rear plate 108 which areinterconnected by bolts 109. The upper weld arm 112 is clamped betweenthe front and rear plates and preferably nests in recesses defined inthe plates. The front plate 107 includes a downwardly extending pivotflange 117 which forms part of the bearing assembly 116. The lower yoke115 is constructed similarly. Specifically, it has a rear plate 118 anda front plate 119, both with recesses in which the lower weld arm 114nests. The rear plate 118 has an upwardly extending pivot flange 120which lays adjacent to the pivot flange 117 of the upper yoke 113. Aswill be clear to those of skill in the art, the pivot flanges areelectrically isolated from one another. However, it can also be seenthat they are relatively cantilever to each other to allow for easydisassembly of the bearing assembly 116.

Referring now to FIGS. 27-30, an eighth embodiment of a modular weldinggun according to the present invention is generally shown at 122. Thistype of welding gun is generally referred to in the industry as a “C” orstraight action welding gun. It has a lower C-shaped arm 123 that holdsan electrode 124. The second electrode 126, is supported by an actuator128. The actuator 128 moves the second electrode 126 with a “straightaction” towards the first electrode 124. This operation is similar tothe way in which a C clamp closes by moving one clamping elementdirectly towards an opposite clamping element. The actuator in theillustrated embodiment is a servo, such as with an internal ball screwarrangement, with an external anti-rotate rod 130. However, as will bediscussed later, other types of actuators may be used in place of theillustrated actuator.

As with the prior embodiments, the gun 122 is made of modular componentswith the lower C-shaped weld arm 123 made of bar stock. The gun 122 isdesigned to be supported by a robot and has a robot mount 132. It isalso designed for use with a remotely mounted transformer. Obviously,the modular construction of a straight action welding gun differs fromthe scissors-type gun discussed earlier. However, similar weld arms suchas lower weld arm 123 may be used with either embodiment. In addition,the remainder of the straight action welding gun 122 is bolted togetheras with the prior embodiment. Specifically, a lower yoke 134 bolts tothe lower arm 123 and also interconnects with the frame 136 whichsupports the actuator 128. As with previous embodiments, the yoke 134comprises a pair of plates which clamp together with the weld arm 123trapped therebetween. In this way, the lower arm may be easily unclampedfrom the yoke 134 and replaced or modified.

Referring now to FIGS. 31-34, a ninth embodiment of a modular weld gunaccording to the present invention is generally shown at 140. This weldgun 140 is a portable “C” or straight action, pneumatically operatedweld gun. Once again, it is assembled from a variety of modularcomponents but differs from the previous embodiment in that it includesa hanger 142 for supporting the portable gun and a pneumatic actuator144 for moving the electrodes together.

Referring now to FIGS. 35-38, the design of a servo actuator, whichrepresents a further aspect of the present invention, will be discussed.The servo actuator is generally shown at 150. The servo actuatorincludes the actuator itself 152 and a drive motor 154. The actuator 152is designed to work with a variety of motors 154 so the illustratedmotor is for illustration purposes only. In fact, the actuator 152includes an adaptor plate 156 that allows the actuator to mount to anyof a variety of servo motors. The actuator includes a centralcylindrical portion which contains the ball screw actuator. Thecylindrical portion 158 is sandwiched between a front housing 160 and arear housing 162 that are interconnected by tie rods 164. The tie rods164 act to clamp the actuator together and allow for easy disassembly.The illustrated front housing 160 has trunnion mounts 166 extending fromthe sides thereof allowing the actuator to be mounted in a trunnion aspart of a scissors type weld gun. The front housing 160 may beinterchanged with a different front housing that allows a differentmounting arrangement. For example, a front housing with mounting holestherein may be provided so that the actuator can be used as part of astraight action gun.

Referring now to FIGS. 39 and 40, the internal workings of the actuatorof FIGS. 35-38 will be described in more detail. As shown, the motor 154turns a drive pulley 168 which in turn rotates a driven pulley 170 via abelt 172. The driven pulley 170 drives a screw 174 which extends throughthe center of the actuator 152. A nut 176 is supported around the screw174 and moves forwardly and backwardly as the screw 174 turns. Thoughnot shown, the screw 174 and nut 176 form a ball screw arrangementwherein balls ride in grooves cut into the screw and nut. A square rod178 mates with the forwardmost end of the nut 176 so that it movesforwardly and backwardly with it. In FIG. 37, the front end of the nut176 and the rear end of the square rod 178 are shown separated by ashort distance for detail. However, in use, the rearward end of thesquare rod 178 would fit over the front end of the nut 176 so that theymove together. Traditional ball screws have problems with the output endof the actuator rotating around the central axis of the ball screw as itmoves forwardly and backwardly. As shown earlier in FIGS. 27-30, a ballscrew servo actuator may include external anti-rotate features.According to the present invention, the square actuator rod 178 has asquare cross-section and passes through a square orifice 180 in thefront housing 160. As best shown in FIGS. 40 and 41, the square orifice180 in the housing 160 is defined by a bearing or bushing 179. Thisbearing or bushing 179 is supported by the front housing 160 and has asquare orifice defined therethrough. As shown, the orifice is elongatedin the direction of the rod so as to create a large support surface. Inone preferred embodiment, the bearing or bushing 179 has an end-to-endlength of three to three and one half inches. In other embodiments, thebushing is also elongated, but may have a length of only two inches ormore, or one inch or more. However, the highly elongated bushing, with alength of three to three and one-half inches or more is preferred. Insome embodiments, the bushing is aluminum with a Rulon® coating. Rulon®is an oil impregnated plastic. The bushing may be made out of othermaterials as well.

Therefore, the actuator rod 178 just moves inwardly and outwardly anddoes not rotate about the central axis of the ball screw. As will beclear to those of skill in the art, the actuator end 182 of the squarerod 178 may have various configurations based on the needs of the weldgun which it is designed to actuate. However, the present configurationof servo actuator 150 allows for interchangeability of parts making iteasier to adapt the actuator to a variety of applications. Also, thesquare actuator rod 178 avoids the need for external anti-rotatefeatures.

Referring now to FIGS. 41 and 42, an alternative embodiment of aservo-actuator is illustrated. Specifically, FIG. 41 shows across-sectional view of a servo-actuator similar to the actuator shownin FIGS. 35-39. The actuator portion 180 is shown in exploded form inFIG. 42 to show the internal construction. This embodiment differs fromthe previous embodiment in that the nut 182 which engages the screw 184is bolted to the end of the square rod 186 and is a somewhat differentshape and size. It can also be seen that the trunnion 188 which definesthe actuator end of the actuator portion 180 includes bolt holes 190 forinterconnecting the trunnion 188, and the actuator, to a welding gun. Asquare bearing or bushing 192 fits into the trunnion 188 and defines thesquare opening in the front of the actuator that prevents rotation ofthe square rod 186. As with the previous embodiment, the bushing iselongated with a preferred length of three to three and one half inchesor more. However, in other embodiments, the bushing may have a length oftwo inches or more or one inch or more. The bushing has a constructionsimilar to the previously discussed bushing. In FIG. 41, a differentmotor 194 is shown driving the actuator 180, although a variety ofmotors may be used.

Referring now to FIGS. 43-46, another configuration of a servo actuator200 is shown. In a previous embodiment of a servo actuator, the trunnionmount was located near the actuator end of the actuator while in theservo actuator 200 in FIGS. 43-46, the trunnion mount 202 is mountedtowards the rear. As will be clear to those of skill in the art, themodular system of the present invention may be adapted for use witheither type of servo actuator.

Referring now to FIGS. 47-50, yet another version of a servo actuator210 is illustrated. In this configuration the servo actuator 210 has aflange 212 for mounting it to a welding gun. The modular approach allowsthis type of actuator to be used as well.

Referring to FIGS. 51-52, yet another embodiment of an actuator for usewith the present invention will be described. The actuator 220 is apneumatic or air-actuated cylinder with anti-rotate features similar tothe previously discussed actuators. As known to those of skill in theart, pneumatic actuators, in a wide variety of designs. The actuator 220illustrated in FIGS. 51 and 52 is a sophisticated 4-port actuatordesign. However, the anti-rotate feature according to the presentinvention is also applicable to other types of pneumatic actuators. Theactuator 220 has an outer housing 222 with a forward end 224. A pistonrod 226 extends out of the forward end 224. As illustrated, the pistonrod 226 has a generally rectangular or square cross-section which meetswith a matching opening in the forward end 224 of the housing 222. Therectangular square opening in the housing may be part of the housing, ora bushing, as illustrated. Another bushing 230 is shown in FIG. 53. Aswill be clear to those of skill in the art, the specific design of thebushing 228 or 230 depends on the application. In some embodiments, thebushing is aluminum with a Rulon® coating. Rulon® is an oil impregnatedplastic. The bushing may be made out of other materials as well. As withthe previous embodiments, it is preferred that the bushing be elongatedwith a Length of 3 to 3½ inches or more. In alternative embodiments, thebushing may have a length of only 1 inch or more, or 2 inches or more.Referring again to FIGS. 51 and 52, it can be seen that the piston rod26 is not required to be square throughout its length. Instead, the tip232 may be shaped so as to interconnect with other items. Also, internalto the actuator 220, the piston rod 226 is typically roundedcross-section, as best shown in FIG. 52. The actuator 220 is a 4-portdesign, including a weld forward port 234, a retract forward port 236, aretract return port 238, and a weld return port 240. Internally, theactuator 220 includes a first piston 242 connected to the piston rodnear its rear end and a second piston 244 connected to the piston 226intermediate its two ends. The first piston 242 moves inside an innercylinder 246, which is movable inside of the housing 222. A separator248 divides the housing 222 into two sections. In operation, compressedair is introduced into the retract forward port 236, which causes theinner cylinder 246 to move forward until it is stopped by the separator248. The first piston 242 and second piston 244, along with a piston rod226, move forwardly with the inner cylinder 246. When compressed air isintroduced into the weld port 234, pressurized air is introduced behindthe first piston 242 and second piston 244 causing them both to moveforwardly, along with the piston rod 226. When compressed air isintroduced into the retract return port 238, the inner cylinder 246 ismoved rearwardly until stopped by the rear cap 250. The first piston242, second piston 244, and piston rod 226 move backwardly with theinner cylinder 246. When compressed air is introduced into the weldreturn port 240, pressurized air is introduced forward of the first andsecond pistons, causing the pistons 242 and 244 to move rearwardly,along with the piston rod 226.

As will be clear to those of skill in the art, the present invention maybe adapted and modified in various ways without departing from theintent or scope of the present invention. It is the following claims,including all equivalents, which define the scope of the presentinvention.

1. An actuator for use with a welding gun of the type having a firstelectrode movable in a straight line toward and away from a secondelectrode supported by a welding arm, the actuator comprising: a housinghaving a first and a second end, said first end having a bushing with agenerally rectangular opening defined therethrough; an actuator rodextending through said square opening in said bushing and having a firstend disposed inside said housing and a second end disposed external tosaid housing, said actuator rod having an external surface with agenerally rectangular cross section such that said external surfaceengages said generally rectangular opening to prevent rotary motion ofsaid rod with respect to said housing; and a drive mechanism disposed insaid housing operable to move said rod with respect to said housing. 2.The actuator according to claim 1, wherein the generally rectangularopening in the bushing is generally square, and the external surface ofthe actuator rod has a generally square cross section.
 3. The actuatoraccording to claim 1, wherein the drive mechanism comprises a pneumaticdrive unit.
 4. The actuator according to claim 1, wherein the drivemechanism comprises a rotary screw driving a drive nut.
 5. The actuatoraccording to claim 1, wherein the generally rectangular opening in thebushing comprises an elongated passage with a generally rectangularcross section, the passage having a length greater than 1 inch.
 6. Theactuator according to claim 1, wherein generally rectangular opening inthe bushing comprises an elongated passage with a generally rectangularcross section, the passage having a length greater than 3 inches.
 7. Anactuator for use with a welding gun of the type having a first electrodemovable in a straight line toward and away from a second electrodesupported by a welding arm, the actuator comprising: a housing having afirst and a second end, said first end having a bushing with a generallysquare opening defined therethrough; an actuator rod extending throughsaid square opening in said bushing and having a first end disposedinside said housing and a second end disposed external to said housing,said actuator rod having an external surface with a generally squarecross section such that said external surface engages said squareopening to prevent rotary motion of said rod with respect to saidhousing; and a drive mechanism disposed in said housing operable to movesaid rod with respect to said housing.